モルタルで擬似した軟岩の流砂の衝突による洗掘

抄録

In order to design the measure against scouring of soft rock, it is necessary to clarify the scouring mechanism of soft rocks. In this research, in order to clarify the scouring mechanism of soft rocks in detail, the hydraulic experiments are conducted at a laboratory. Since it was impossible to install the soft rocks in a flume without disturbing in the flume, the poor mixing mortar was used instead of the soft rock. The pebble whose particle diameter is 4.36 mm as a gravel leading to scouring was used. In order to grasp the mechanism of the scouring, three cases to which the supplying amount of the gravel from upstream end of the flume was changed were performed. In this experiment, it became clear that scouring of mortar arose by the collision of gravel rather than that is caused by friction of gravel. Then, to formulize scouring by the collision of gravels was tried. It was assumed that total of the collision energy to the mortar of a gravel is proportional to the amount of scouring of mortar. The proportionality constant in this formula was obtained by the experiment which made the glass ball collide with this mortar directly. The computed scouring depth using the hydraulic conditions and the proportionality constant is reproducing the result of hydraulics experiment with sufficient accuracy, although there is a tendency of an underestimate a little. From the above result, it becomes clear that there are two kinds of scouring mechanisms of soft rocks. One is abrasion by friction of gravels and another is damage by the collision of gravels. Furthermore, it becomes clear that the scouring mechanism changes with saltation length of a gravel. That is, the scouring factor is the collision of a gravel when the saltation length is larger than the diameter of a gravel, and the factor is the friction of a gravel when the saltation length is smaller than the diameter.